The present invention relates to the field of dyeing. More particularly, the present invention relates to the field of dyeing polymeric fibers. Even more particularly, the invention relates to the field of dyeing polymeric fibers which have limited dye sites and/or difficult to penetrate chemical structures.
Polymeric fibers are used in a wide variety of applications. For example, fibers made from nylon can be formed into yarns that have wide application in textiles and carpets. One advantage of nylon is the fact that it is readily dyeable. In particular, the amine groups in the nylon polymer accept dye molecules known in the industry as acid dyes. The amine groups are thus "dye sites" for the nylon fibers. Techniques are known for dyeing nylon yarns wherein the complete yarn is dyed to a uniform color. In addition, techniques are know for space dyeing nylon yarn. In space dyeing, one or more colors of dye are applied at intermittent spaces along the length of the yarn. Space dyed nylon yarns are especially popular in carpet manufacture where they can provide a desired visual effect.
Techniques are also known for printing on fabrics or carpets made of nylon fibers. In particular, techniques are known for selectively placing one or more colors of dye on or in the fabric or carpet in a predetermined pattern.
In order to make nylon fibers stain resistant, techniques have been developed for blocking the dye sites on nylon fibers. In these techniques, the fibers are treated with a compound which blocks the amine groups on the nylon fibers to thereby make them unavailable as dye sites. As a result, stain molecules are prevented from attaching to the fibers, and the product can be promoted as stain resistant. This kind of treatment is particularly popular for nylon carpets. Specific examples of this treatment are known as WEARDATED by Monsanto, STAINMASTER by DuPont, and WORRY FREE by Allied.
Most stain resist treatments are presently added to the formed yarns or the carpet, and thus do not interfere with the dyeing of the fibers or yarns. However, some stain resist treatments, such as LUMINA by DuPont are included in the polymer melt. Thus, the pigment dyeing of such fibers will typically have to take place in the melt, thereby limiting the applicability of space dyeing or printing. In addition, if the stain resist treatment is applied to the yarn before tufting, the applicability of printing on the carpet is also limited.
The polyolefins, and particularly polypropylene, have experienced a growing popularity for use in fibers. The relatively low cost of polypropylene makes it especially attractive for carpets, upholstery fabrics, draperies and apparel fabrics.
One problem with using polypropylene is the fact that its structure is relatively inert and difficult to penetrate. The structure of polypropylene does not include dye sites. Consequently, the acid dyes typically used on nylon fibers could not generally be used to dye polypropylene.
One method of coloring polypropylene fibers is to use what is known as solution dyeing. In this process, the pigment is added directly to the polypropylene melt before the fibers are formed. A drawback of solution dyeing is that the fibers and yarns so produced all have the same color through their whole length. Naturally, solution dyeing cannot be used for space dyeing yarns or printing on fabrics or carpets.
Another method of coloring polypropylene fibers is to chemically modify the polymer with a chemical additive which will share electrons with a specially manufactured dye which contains a transition metal such as nickel, thus forming a coordination compound when heat is applied. This system is known as the nickel chelating system. Unfortunately, this system has the drawbacks of requiring a specially modified fiber, typically providing only dull metallic shades, and the production of water polluting effluents due to the presence of heavy metals.